[Footnote 65: The battle of Champigny had extended our lines to four thousand six hundred and twenty yards from the Fort de la Faisanderie.] EXPLANATION OF SOME OF THE TECHNICAL TERMS USED IN THIS BOOK. AGGER (Latin), terrace, or platform, which the Romans raised before the fronts attacked, for the purpose of setting up their projectile machines, securing a commanding position, and masking the troops assembled for an assault. BAILEY, fore-court; court of the outer works, or yard. The stables and the lodgings for the garrison were usually disposed in the bailey of the strong castles of the Middle Ages (see p. 169). BALISTA (Latin, _onager_), an engine for propelling stones, worked by means of strongly-twisted cords. BARBICAN, exterior defence protecting an entrance, and allowing a large assemblage of men to prepare for sorties, or to protect a retreat. Barbicans were either of masonry or earth, or constructed of a simple palisade. They were always of a circular form (see p. 169). BASTION, an earthwork, cased externally with masonry, salient beyond the main body of the fortress, and possessing two faces, two flanks, and a gorge, so as to sweep the ground without, to cross the fires, and to flank the curtains. The gorge of bastions is open, closed, or retrenched. Bastions are said to be full when their _terre-plein_ is level with the curtains; empty, when their _terre-plein_ is beneath that level; armed with a cavalier, when upon their _terre-plein_ is raised a battery of earth which commands the country without over the parapets (see p. 278, 310). BOULEVARD, an earthwork--in use at the time when fire artillery had attained a certain degree of importance--for placing cannon outside ancient defences still preserved. Boulevards were of all forms--square, circular, and triangular (see p. 229). BRAIE, an exterior defence of trifling height, protecting the foot of the ramparts, and hindering the enemy's approach. BRETÈCHE, timber construction intended to strengthen and to flank a front or a salient (see p. 184). CAT, timber gallery, low and long, covered with a longitudinal very pointed and strongly ironed roof. Placed on wheels, these galleries were advanced to the foot of the walls, after the ditch was filled up, and enabled the miners to begin working into the masonry under cover. The name _rat_ was given to these galleries in some provinces. CATAPULT, engine for shooting large darts by means of a powerful bow. CAVALIER, earthwork raised in the middle of a bastion, or upon any point of the defence, to command the exterior. In the sixteenth century the besieging armies erected cavaliers around defences to mount cannon upon them. Our siege batteries are the modern analogues of these works (see p. 237, 312).